Fixation of leuco vat ester dyes by electrical current

ABSTRACT

LEUCO VAL ESTER DYES ARE FIXED ONTO CELLULOSIC OR POLYESTER TEXITLE BY ELECTRICAL ENEGY. THE LDYESTUFF IS APPLIED TO THE TEXTILE FIBROUS SUBSTRATE IN AN AQUEOUS SOLUTION AND THE TEXTILE IS SUBJECTED TO DIRECT CURRENT FROM SEPARATE ELECTRODES. DESIRABLY, THE DYED SUBSTRATE IS DRIED AND HEATED TO CAUSE FINAL FIXATION.

United States Patent "ice 3,758,394 FIXATION 0F LEUCO VAT ESTER DYES BY ELECTRICAL CURRENT Kurt A. Dellian, Spring Valley, N.Y., assignor to Ciba- Geigy Corporation, Greenburgh, N.Y.

No Drawing. Continuation-impart of abandoned application Ser. No. 864,049, Oct. 6, 1969. This application May 27, 1971, Ser. No. 147,685

Int. Cl. Btllk 1/00; (307!) 29/06 US. Cl. 204-134 7 Claims ABSTRACT OF THE DISCLOSURE Leuco vat ester dyes are fixed onto cellulosic or polyester textile -by electrical energy. The dyestuff is applied to the textile fibrous substrate in an aqueous solution and the textile is subjected to direct current from separate electrodes. Desirably, the dyed substrate is dried and heated to cause final fixation.

RELATED APPLICATION This application is a continuation-in-part of Ser. No. 864,049, entitled Electrolytic Fixation of Reactive Dyes, filed Oct. 6, 1969, now abandoned.

BACKGROUND OF THE INVENTION The present invention is directed to a technique for dyeing or printing material of cellulosic origin and cellulosic-synthetic blends with leuco vat dyestufl's.

It is known in the prior art that leuco vat ester dyestuifs may be employed for dyeing and printing cellulosic fibers. Unfortunately, there are disadvantages in the wellknown technique of dyeing or printing with this type of dye. Ordinarily, the dyestufi is developed by acid in the presence of an oxidizing agent, as for example, sulfuric acid and sodium nitrate. Several diiferent methods and techniques exist in application of the leuco vat ester dye but there is a common procedure to diflferent embodiments. The dye is first applied to the substrate textile goods through exhaustion as from a dyebath or via padding on a continuous range. Thereafter, the wedded textile and dye is submitted to an oxidation process under acid conditions conventionally using sulfuric acid and sodium nitrate or alkali chromates to develop the original vat dye. After this two-step chemical bath treatment, a heat treatment, as steaming, is employed to cause fixation.

One of the disadvantages of the prior art technique of applying the leuco vat dye is that the two-step operation is essential. Additionally, intermediate drying of the padded goods between the two separate steps often causes streaking or two-sidedness.

The leuco vat dye is not applied and fixed in a single operation because the acid which is essential would saponify the dye ester and with an oxidizing agent Would cause reoxidation and returun to the original vat dye.

Therefore, the stability of a one-step bath containing the leuco ester dye, acid and oxidizing agent for application and fixation of the dye would be poor and, practically, such technique is not employed.

The prior art teaches in British Pat. 875,364 the use of an electric current in the presence of an electrolyte to cause fixation of a reactive dyestuff. However, this patent employs an entirely different dyestufi from the present invention and the patent discloses the criticality of an added electrolyte.

It is an object of the present invention to apply a leuco 3,758,394 Patented Sept. 11, 1973 vat ester dye to a substrate without the need for two separate baths and without intermediate drying.

It is a further object of the present invention to employ an electrical technique to replace the use of a bath containing both oxidizing agent and an acid.

SUMMARY OF THE INVENTION Leuco vat ester dyes are applied to a textile fiber of cellulosic origin and/or polyester by nipping or printing with an aqueous solution of the dyestuff. The present technique bypasses the need for use of a second bath which contains an oxidizing agent in an acid environment. Instead of this chemical utilization, an electrical treatment is employed replacing the second bath treatment of the prior art. The textile, containing the applied aqueous leuco vat dye, is contacted with an anode and cathode carrying direct current. Thereafter, to fully fix the dye on the textile, a drying and heating procedure desirably is used which causes complete transformation of the leuco vat ester dye to its original vat dye.

DETAILED DESCRIPTION OF THE INVENTION The present technique involves the application to a fibrous textile of cellulosic nature, polyester, and blends thereof. As employed herein, cellulose includes regenerated cellulose such as rayon. Textile in the present application is used in its normal context and would exclude a paper substrate. As employed herein, a fibrous material includes fibers, yarns, threads, fabric, ribbons and tabs. This invention bypasses the need for use of a two-step application technique of leuco vat ester dyes and bypasses the need in the two-step technique of use of a bath maintained under acid conditions containing an oxidizing agent.

The type of dyestuff necessary for application in this disclosure is a leuco vat ester dye. These dyes are derived from vat dyestuffs by reducing and esterification of the leuco compound which is commonly achieved with sulfuric acid in the presence of pyridine. These dyestuffs well know in the art are listed in the Color Index under Cl. solubilized vats.

The dyestufis is used in an aqueous solution such as from a bath. The technique of printing or dyeing involving initial application of the leuco vat dyestutf may be by well known techniques in the prior art. Illustratively, the dye in an aqueous solution may be padded, nipped, or printed onto the substrate. The pH solution conventionally would be near neutral such as 6.5 to 7.5.

An important and critical feature in this disclosure is the use of electrical energy to replace the previously employed oxidative treatment under acid conditions of the fiber containing the dyestutf. Illustratively, the fiber is first padded with an aqueous solution of the leuco vat dye. Thereafter, the padded and wet material is subjected to electrical energy involving direct current by contact with anode and cathode members which cause electrolytic fixa tion of the dye.

The various arrangements of the electrodes and the types of electrodes to apply the respective opposite charges does not per se form a specific portion of this invention. Various modifications of suitable apparatus will be readily evident to one skilled in the art. Illustratively, point, roller, plate, and belt electrodes or combinations thereof may be employed. These electrodes may be positioned on opposite sides of the fiber or adjacent to one another on the same side of the fiber. Various embodiments of the appropriate apparatus are exemplified in parent application Ser. No. 864,049.

The electrodes may be of various materials, such as metals, which serve as conductors. The electrodes will be isolated from one another and will not be grounded since otherwise the charge from each electrode will not be transferred to the textile fiber.

The strength of current utilized may vary within wide limits, such as between 0.1 to 500 amperes and, more preferably, 0.5 to 100 amperes. However, the above current strength is considered illustrative since, for example, the residual time the fiber is subject to respective anode and cathode portions is a determining factor. Since the fibrous material would normally be passed between the electrodes in continuous manner, the contact or residence time of the material aids in determining the current employed. For example, with long contact times with the fiber travelling slowly, the residence time of the substrate portions within the influence of the electrode charges will be relatively long in comparison with fiber travelling at a fast speed past the electrodes. Additionally, the type of electrodes, for example, plate as opposed to point, and the weight and thickness of the fabric will additionally influence the strength of the current employed.

The reactivity of the particular leuco vat ester dye will also influence the strength of the direct current employed.

During the fixation process, the anode and cathode portions may remain unchanged or they can be changed by reversing the direction of the current. However, the use of an alternating current source connected to the electrodes is considered to lie outside the scope of the present disclosure. The rapid alternation of this current source is undesirable for the fixation of the leuco vat dye. Also, various combinations of electrode positioning as well as combinations of electrode types may be employed. Varying embodiments are illustrated more fully in the parent application Ser. No. 864,049.

In the aqueous leuco vat dye that is applied to the substrate, the use of an added electrolyte to aid in carrying the electric current is totally unnecessary. For example, in a dyebath, no added electrolyte such as a salt need be employed.

Since an electrolyte added to the aqueous leuco vat dye need not be employed, undesirable by-products are not formed when the electric current is passed to cause fixation of the dye. Illustratively, sodium chloride as an added salt to the dyebath causes chlorine gas to be formed at the anode, which gas would be vented to the atmosphere.

After the electrical treatment of the leuco vat dye on the fiber, the textile is dried. Thereafter, heating takes place to cause complete transformation of the leuco vat dye to its original vat dye and to cause final fixation on the substrate. The treatment temperature will be determined by the reactivity of the dyestufi employed. Treatment tem peratures may range from 180 F. to 500 F. and, more preferably, 220' to 300 F. In the case of polyester fibers and blends thereof, temperatures of 400 to 425 C. have been found desirable for optimum results. Heating times may vary within wide limits and generally will be at least one-half minute. Heating times beyond about five minutes are unnecessary, although longer times will be employed. Heating temperatures and heating times will be determined partially by the reactivity of the original leuco vat ester dye employed, the substrate, and the combination of dyesubstrate.

As set forth previously, the dyeing and printing process herein can be employed for combinations of the cellulosic or regenerated cellulose and polyesters as well as for the individual material. The fastness of the dyestuifs dyed or printed in accordance with this disclosure, utilizing electric current passed through anode and cathode members, is as good as the fastness of the same dyestuffs dyed or printed according to known processes.

To further illustrate the innovative aspects of the present invention, the following examples are provided:

4 Example 1 A fabric of mercerized cotton is padded with an aqueous padding liquor containing 30 g./l. of the dyestuffs of the formula:

O-SOaNa NBDaS-O Example 2 A fabric of mercerized cotton is dyed according to procedure of Example 1, but using a dyestuff of the following formula:

NaOgS-Z (B \GZO/ A brilliant deep violet is formed with the same properties as it would result by usual dyeing methods.

Example 3 A fabric of mercerized cotton is padded with an aqueous padding liquor containing 30 g./l. of the dyestuff of the following formula:

NaOaS-O and 1 g./l. of the sodium salt of 1.7 tri-isobutyl-naphthalene-3-sulfonic acid. The padded and wet material is located between two stainless steel plates in the form of a sandwich. The steel plates are respectively connected to an anode and cathode and exposed to direct current of 6 volts and 10 sec. After drying the fabric, cure for 2 minutes at 320 F. A deep red shade is formed after rinsing and soaping.

Example 4 A fabric of a blend of parts polyester and 35 parts cotton is submitted to a procedure as described in Example 2, but the curing time is 1 minute at 420 F. Both fibers are dyed with good fastness properties.

Although the present invention has been shown and described with reference to particular embodiments, it

is understood the invention is defined only by the scope of the attached claims.

5 6 What is claimed is: 7. The process of claim 4 wherein said fibrous textile 1. A process for fixation of leuco vat ester dyestulfs comprises polyester and said temperature is 400 to soluble in aqueous dyebath liquor on a fibrous textile of 425 F. cellulose, polyester, and blends thereof comprising con- References Cited tacting said material with an aqueous liquor containing 5 UNITED STATES PATENTS leuco vat ester dyes and then contacting said material with electrodes and passing a direct electrical current 1 02 40 4 9 Ewing et 1 2 4 7 through said material, whereby said leuco vat ester dye 2 371 145 3 1945 Brubaker o is simultaneously saponified and oxidized and converted 51 03 970 spatz et 1 0 X into a water insoluble vat dyestutf by such direct elec- 10 trical current thereby fixing said dyestuif on said material. FOREIGN PATENTS 2. The process of claim 1 wherein said liquor is free of an added electrolyte. 23,827 1898 Great Britain 204134 3. The process of claim 1 wherein the direct electrical 587,540 4/1947 Great Britain 204-134 current has a strength of 0.1 to 100 amperes. 15 864,988 1/ 1953 Germany 204-134 4. The process of claim 1 wherein said fixed dyestuif is subjected to elevated temperature to cause transforma- FREDERICK EDMUNDSON, Primary Examlnel' tion to a vat dyestutf.

5. The process of claim 4 wherein said temperature comprises 180 to 500 F. 20

6. The process of claim 4 wherein said temperature comprises 220 to 350 F. 

